The engine coolant temperature (ECT) sensor is a thermistor that varies resistance
according to changes in engine coolant temperature. The PCM supplies a 5 volt
reference through a pull-up resistor to the sensor, which is connected to ground.
When the sensor is cold, it has a high resistance, high signal voltage at the PCM.
As the sensor temperature increases, its resistance decreases, lower signal voltage
at the PCM. The PCM uses the signal voltage to determine engine coolant temperature.
DTC P0128 sets when the calculated accumulated airflow exceeds the predicted
accumulated airflow when the engine coolant temperature has reached a calibrated temperature.
More air will flow through a cold engine then when the engine is warm.
Conditions for Setting the DTC
DTC P0128 will set if the calculated accumulated airflow has been exceeded,
based on predicted airflow, when the ECT sensor temperature has reached 70°C (158°F)
when:
| • | The vehicle has traveled greater than 2.4 km (1.5 miles)
when the vehicle speed is above 40 km/h (25 mph). |
| • | Engine run time is between 30 seconds and 30 minutes. |
| • | Startup ECT is less than 65°C (149°F). |
| • | IAT is greater than -7°C (19°F). |
| • | Calculated average air flow is greater than 20 g/s. |
| • | No CKP, ECT, EVAP leak, fan control, fuel injector, fuel trim, IAT, MAP,
misfire, TP, vehicle speed, P0130, P0602, or P1621 DTCs have been set. |
